CN116117152B - Preparation method of iron-based micro powder with high magnetic conductivity and low high frequency loss - Google Patents

Abstract

The invention discloses a preparation method of iron-based micro powder with high magnetic conductivity and low high frequency loss, and belongs to the technical field of soft magnetic material preparation. The method takes ferrous carbonate as a precursor, and prepares the micron-sized aluminum oxide coated iron powder with controllable properties by high-temperature hydrogen reduction after air oxidation and aluminum oxide coating. From a composition point of view, a higher degree of reduction and a smaller coating ensure a high content of elemental iron, which is advantageous for achieving a higher permeability. From the structural point of view, larger grain size is beneficial to reducing hysteresis loss, stable alumina insulating layer is beneficial to isolating conductive paths, reducing inter-particle eddy current, and the formation of internal pore structure is beneficial to inhibiting intra-particle eddy current. The magnetic ring sample prepared by the micron-sized aluminum oxide coated iron powder has higher magnetic permeability in the range of 1-30 MHz, lower loss above 16 MHz and better comprehensive performance than the carbonyl iron powder product with high magnetic permeability sold in the market. The process of the invention is nontoxic and harmless, has good reproducibility, and is suitable for large-scale industrial production.

Description

A method for preparing iron-based micropowder with high magnetic permeability and low high-frequency loss

Technical Field

The invention belongs to the technical field of soft magnetic materials, and in particular relates to a method for preparing metal soft magnetic micropowder.

Background technique

Inductors made of soft magnetic composite materials based on magnetic metal micropowders are widely used in high-frequency consumer electronic devices. However, with the further increase in the switching frequency of the above-mentioned devices, the eddy current loss of traditional iron-based soft magnetic composite materials has increased significantly and the magnetic permeability has decreased significantly. To solve this problem, researchers currently mainly start from the following two aspects. First, oxides are used to insulate the surface of magnetic powders, thereby effectively blocking the eddy current path between magnetic powders, reducing eddy current losses, and maintaining good frequency stability of magnetic permeability. Although this method can regulate the eddy currents between magnetic powders by adjusting the thickness of the oxide insulating layer, some oxide insulating layers may be damaged after pressing and annealing, resulting in the enhancement of eddy currents between particles and the increase of eddy current losses. Secondly, by reducing the size of magnetic powder particles, the eddy currents inside the magnetic powder can be suppressed to achieve a reduction in eddy current losses. However, there are many shortcomings in the preparation process of small-sized (especially below 10 µm) magnetic metal micropowders. Among them, the production of high magnetic permeability carbonyl iron powder requires high pressure equipment with high pressure and high temperature, and the production process involves a variety of hazardous materials, which is extremely dangerous; and the production of alloy magnetic powder with lower magnetic permeability than carbonyl iron powder usually adopts atomization process, but the powder yield of alloy magnetic powder particles below 10 µm is low and the cost is very high. Therefore, the development of non-toxic, harmless, reproducible and efficient preparation processes to prepare iron-based metal micropowders with stable insulating layers and controllable structures, so that they have the characteristics of high magnetic permeability and low high-frequency loss in the high-frequency range, has become the focus of current research.

Summary of the invention

In order to solve the problem of low magnetic permeability and high loss of iron-based metal powder for high frequency, the present invention provides a method for preparing iron-based powder with high magnetic permeability and low high-frequency loss.

The preparation steps of an iron-based micropowder with high magnetic permeability and low high-frequency loss are as follows:

(1) Preparation of micron-sized iron oxide (Fe ₂ O ₃ ) powder

(1.1) Mix equal volumes of glycerol and deionized water and divide the mixture into two solutions, namely solution A and solution B;

Dissolve 1.06 g of anhydrous sodium acetate in 25 ml of solution A to obtain anhydrous sodium acetate solution; dissolve 1.99 g of ferrous chloride tetrahydrate in 25 ml of solution B to obtain ferrous chloride tetrahydrate solution;

Under magnetic stirring conditions, anhydrous sodium acetate solution was added dropwise to ferrous chloride tetrahydrate solution to form a gray-green mixture; the mixture was kept in a reactor at 180°C for 12 h; the mixture was cooled, magnetically separated, washed with ethanol, and washed with deionized water to obtain a brown precipitate; the brown precipitate was vacuum dried at 50°C to obtain micron-sized ferrous carbonate (FeCO ₃ ) powder; the ferrous carbonate powder was brown-brown, the powder particles were spherical, and the particle size was 6-8 µm;

(1.2) Micron-sized ferrous carbonate (FeCO ₃ ) powder was heated to 700°C in air at a heating rate of 5°C/min, kept at this temperature for 3 h, and cooled naturally to obtain reddish-brown micron-sized iron oxide (Fe ₂ O ₃ ) powder with a particle size of 5-7 µm;

(2) Preparation of micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder

(2.1) 0.2 g of aluminum nitrate nonahydrate was dissolved in 100 ml of ethanol to obtain an aluminum nitrate nonahydrate solution; 1 g of reddish brown micron-sized iron oxide (Fe ₂ O ₃ ) powder was added to the aluminum nitrate nonahydrate solution and mechanically stirred to obtain a mixed material C; 1 g of anhydrous sodium carbonate was dissolved in 25 ml of deionized water and added dropwise to the mixed material C, the pH value was adjusted to 4, the mixture was reacted for 4 h, magnetic separation was performed, ethanol washing was performed, and deionized water washing was performed to obtain a reddish brown micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder; the micron-sized alumina-coated iron oxide powder was composed of iron oxide (Fe ₂ O ₃ ) and aluminum oxide (Al ₂ O ₃ ), the mass fraction of iron element was 64-66 wt %, the mass fraction of aluminum element was 0.5-1.5 wt %, and the mass fraction of oxygen element was 32-35 wt %; the particles of the micron-sized alumina-coated iron oxide powder were spherical and had a particle size of 5-7.5 µm;

(2.2) placing the micron-sized aluminum oxide-coated iron oxide powder in a flowing hydrogen atmosphere, heating the temperature to 400-700 °C at a heating rate of 5 °C/min, and keeping the temperature for 4 h; cooling the mixture naturally to obtain a micron-sized aluminum oxide-coated iron (Fe@Al ₂ O ₃ ) core-shell powder;

The micron-sized alumina-coated iron powder is composed of iron and an alumina (Al ₂ O ₃ ) coating layer, the mass fraction of the iron element is 75-95 wt %, the mass fraction of the aluminum element is 2.5-4.0 wt %, the mass fraction of the oxygen element is 5.5-11.5 wt %, the powder particles are spherical, and the particle size is 5-7 μm. The particle surface of the micron-sized alumina-coated iron powder is rough and has a pore structure, and the pore size is 10-80 nm;

The soft magnetic composite material magnetic ring is prepared by pressing and coating iron powder and resin powder with micron-grade alumina in a mass ratio of 1:1. At a voltage of 1 V, the magnetic permeability is 12.85-15.59 in the frequency range of 1-30 MHz; the magnetic loss factor is 0.008-0.013 in the frequency range of 16-30 MHz.

The further technical solution is as follows:

In step (2), the speed of mechanical stirring is 400 r/min, and the material temperature is maintained at 50 °C.

Compared with the prior art, the beneficial technical effects of the present invention are embodied in the following aspects:

The present invention first prepares micron-sized ferrous carbonate powder by a hydrothermal method, and then uses high-temperature air oxidation to obtain micron-sized iron oxide powder with high purity, uniform particle size and high sphericity. Among them, the hydrothermal process can ensure that the powder particles have excellent particle size uniformity and high sphericity, which is conducive to the uniformity of the subsequent coating process and hydrogen reduction process, and ensures the particle uniformity of the final product. The high-temperature air oxidation process can effectively remove the carbon element in the ferrous carbonate, thereby avoiding the presence of carbon materials in the final product, and avoiding the problem of carbon materials reducing magnetic permeability and increasing magnetic loss. Then, alumina coating is performed by a liquid phase method. Among them, the alumina coating layer can effectively maintain the structural stability of the spherical particles and avoid the problem of particle agglomeration during the high-temperature hydrogen reduction process. Finally, a micron-sized alumina-coated iron powder is obtained through a hydrogen reduction process at different temperatures. From the perspective of magnetic permeability, a high content of iron element is conducive to improving the saturation magnetization intensity, a larger grain size is conducive to reducing the coercive force, and the presence of the alumina insulating layer and the pore structure is conducive to suppressing the high-frequency eddy current effect, and has a higher magnetic permeability in the MHz frequency band. From the perspective of loss, the aluminum oxide (Al ₂ O ₃ ) insulating layer can effectively cut off the conductive path between particles, greatly reducing the eddy current between particles, and the formation of the pore structure can also effectively weaken the eddy current within the particles. Therefore, the magnetic ring sample prepared by the micron-sized aluminum oxide coated iron (Fe@Al ₂ O ₃ ) powder has a magnetic permeability of 12.85-15.59 in the frequency range of 1-30 MHz at a voltage of 1 V, and a magnetic loss factor as low as 0.008-0.013 in the frequency range of 16-30 MHz, showing excellent characteristics of high magnetic permeability and low high-frequency loss.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a scanning electron microscope (SEM) photograph of micron-sized spherical ferrous carbonate (FeCO ₃ ) powder prepared in Example 1;

FIG2 is a scanning electron microscope (SEM) photograph of the micron-sized spherical iron oxide (Fe ₂ O ₃ ) powder prepared in Example 1;

FIG3 is an X-ray diffraction (XRD) spectrum of the micron-sized spherical iron oxide Fe ₂ O ₃ powder prepared in Example 1;

FIG4 is a scanning electron microscope (SEM) photograph of the micron-sized aluminum oxide-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder prepared in Example 1;

FIG5 is an X-ray energy spectrum (EDS) diagram of the micron-sized aluminum oxide-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder prepared in Example 1;

FIG6 is a scanning electron microscope (SEM) photograph of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 1;

FIG7 is an X-ray diffraction (XRD) spectrum of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 1;

FIG8 is an X-ray energy spectrum (EDS) diagram of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 1;

FIG9 is a scanning electron microscope (SEM) photograph of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 2;

FIG10 is an X-ray diffraction (XRD) spectrum of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 2;

FIG11 is an X-ray energy spectrum (EDS) diagram of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 2;

FIG12 is a scanning electron microscope (SEM) photograph of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 3;

FIG13 is an X-ray diffraction (XRD) spectrum of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 3;

FIG14 is an X-ray energy spectrum (EDS) diagram of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 3;

FIG15 is a diagram showing the element contents of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powders prepared in Examples 1, 2, and 3;

FIG16 is a hysteresis loop diagram of the magnetic rings obtained in Examples 1, 2, and 3;

FIG17 is a density diagram of the magnetic rings obtained in Examples 1, 2, and 3;

FIG18 is a magnetic spectrum diagram of the magnetic rings obtained in Examples 1, 2, and 3;

FIG. 19 is a graph showing the magnetic loss factor of the magnetic rings obtained in Examples 1, 2, and 3.

Detailed ways

The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

Example 1

The preparation steps of an iron-based micropowder with high magnetic permeability and low high-frequency loss are as follows:

(1) Preparation of micron-sized iron oxide (Fe ₂ O ₃ ) powder

(1.1) Mix equal volumes of glycerol and deionized water and divide the mixture into two solutions, namely solution A and solution B;

Dissolve 1.06 g of anhydrous sodium acetate in 25 ml of solution A to obtain anhydrous sodium acetate solution; dissolve 1.99 g of ferrous chloride tetrahydrate in 25 ml of solution B to obtain ferrous chloride tetrahydrate solution; add the anhydrous sodium acetate solution dropwise to the ferrous chloride tetrahydrate solution under magnetic stirring to form a gray-green mixture; keep the mixture in a reactor at 180°C for 12 h; cool, separate magnetically, wash with ethanol, and wash with deionized water to obtain a brown precipitate; vacuum dry the brown precipitate at 50°C to obtain micron-sized ferrous carbonate (FeCO ₃ ) powder; the ferrous carbonate powder is brown-brown, and the particles of the ferrous carbonate powder are spherical with a particle size of 6~8 µm.

(1.2) Micron-sized ferrous carbonate powder was heated to 700 °C in air at a heating rate of 5 °C/min and kept at that temperature for 3 h. The mixture was then cooled naturally to obtain reddish-brown micron-sized iron oxide (Fe ₂ O ₃ ) powder with a particle size of 5-7 µm.

(2) Preparation of micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder

(2.1) 0.2 g of aluminum nitrate nonahydrate was dissolved in 100 ml of ethanol to obtain an aluminum nitrate nonahydrate solution; 1 g of reddish brown micron-sized iron oxide powder was added to the aluminum nitrate nonahydrate solution and mechanically stirred to obtain a mixed material C; 1 g of anhydrous sodium carbonate was dissolved in 25 ml of deionized water and added dropwise to the mixed material C, the pH value was adjusted to 4, the reaction was performed for 4 h, magnetic separation was performed, ethanol washing was performed, and deionized water washing was performed to obtain a reddish brown micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder; the micron-sized alumina-coated iron oxide powder was composed of iron oxide and aluminum oxide, the mass fraction of iron element was 67.37 wt%, the mass fraction of aluminum element was 2.85 wt%, and the mass fraction of oxygen element was 29.78 wt%; the powder particles were spherical and the particle size was 5~7.5 µm.

(2.2) Place the micron-sized alumina-coated iron oxide powder in a flowing hydrogen atmosphere, heat the temperature to 500 °C at a heating rate of 5 °C/min, and keep it at that temperature for 4 h; then cool it naturally to obtain micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder.

FIG1 is a SEM photograph of the micron-sized ferrous carbonate (FeCO ₃ ) powder prepared in Example 1. It can be seen that the prepared powder is composed of spherical particles with a relatively rough surface and a particle size of 6 to 8 μm.

FIG. 2 is a SEM photograph of the micron-sized iron oxide (Fe ₂ O ₃ ) powder prepared in Example 1. It can be seen that the prepared powder is still composed of spherical particles with a particle size of 5 to 7 μm.

FIG3 is an XRD spectrum of the micron-sized iron oxide (Fe ₂ O ₃ ) powder obtained in Example 1. It can be seen that the diffraction peaks are relatively sharp, indicating that the powder has a high degree of crystallinity. The diffraction peaks at 24.1°, 33.1°, 35.6°, 40.9°, 49.5°, 54.0°, 57.6°, 62.4°, 64.0° and 71.9° are characteristic diffraction peaks of Fe ₂ O ₃ , indicating that the powder after high-temperature air oxidation is Fe ₂ O ₃ .

FIG4 is a SEM photograph of the micron-sized aluminum oxide-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder prepared in Example 1. It can be seen that the coated particles are still spherical, with a particle size of 5 to 7.5 μm.

Figure 5 is an EDS image of the micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder prepared in Example 1. It can be seen that the Al and O elements are evenly distributed on the surface of the particles, indicating that a uniform Al ₂ O ₃ coating layer has been formed on the surface of the Fe ₂ O ₃ particles. In addition, the elemental analysis results show that the mass fraction of the Fe element in the micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder is 65.38 wt%, the mass fraction of the Al element is 0.85 wt%, and the mass fraction of the O element is 33.78 wt%.

Figure 6 is a SEM photograph of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 1. It can be seen that the powder is still composed of spherical particles, but due to the high-temperature hydrogen reduction, a large amount of oxygen elements escape, so the particle size is reduced to about 5.5-7.0 μm.

Figure 7 is the XRD spectrum of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 1. It can be seen that the diffraction peaks are sharp, indicating that the powder has high crystallinity. The diffraction peaks at 44.7°, 65.0° and 82.3° are characteristic diffraction peaks of Fe, and no other diffraction peaks appear, indicating that under the reduction action of high-temperature hydrogen, Fe ₂ O ₃ has been successfully reduced to Fe elemental substance.

Figure 8 is an EDS image of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 1. It can be seen from the figure that after high-temperature hydrogen reduction, a uniform Al ₂ O ₃ insulating layer still exists on the surface of the spherical particles, which also shows that the introduction of the Al ₂ O ₃ coating layer can greatly improve the structural stability of the powder in high-temperature hydrogen.

Example 2

The preparation steps of an iron-based micropowder with high magnetic permeability and low high-frequency loss are as follows:

(1) Preparation of micron-sized iron oxide (Fe ₂ O ₃ ) powder

(1.1) Mix equal volumes of glycerol and deionized water and divide the mixture into two solutions, namely solution A and solution B.

Dissolve 1.06 g of anhydrous sodium acetate in 25 ml of solution A to obtain anhydrous sodium acetate solution; dissolve 1.99 g of ferrous chloride tetrahydrate in 25 ml of solution B to obtain ferrous chloride tetrahydrate solution; under magnetic stirring, add the anhydrous sodium acetate solution dropwise to the ferrous chloride tetrahydrate solution to form a gray-green mixture; keep the mixture in a reactor at 180°C for 12 h; cool, separate magnetically, wash with ethanol, and wash with deionized water to obtain a brown precipitate; vacuum dry the brown precipitate at 50°C to obtain micron-sized ferrous carbonate (FeCO ₃ ) powder; the ferrous carbonate powder is brown-brown, and the particles of the ferrous carbonate powder are spherical with a particle size of 6~8 µm.

(1.2) Micron-sized ferrous carbonate powder was heated to 700 °C in air at a heating rate of 5 °C/min and kept at that temperature for 3 h. The mixture was then cooled naturally to obtain reddish-brown micron-sized iron oxide (Fe ₂ O ₃ ) powder with a particle size of 5-7 µm.

(2) Preparation of micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder

(2.1) 0.2 g of aluminum nitrate nonahydrate was dissolved in 100 ml of ethanol to obtain an aluminum nitrate nonahydrate solution; 1 g of reddish brown micron-sized iron oxide powder was added to the aluminum nitrate nonahydrate solution and mechanically stirred to obtain a mixed material C; 1 g of anhydrous sodium carbonate was dissolved in 25 ml of deionized water and added dropwise to the mixed material C, the pH value was adjusted to 4, the reaction was performed for 4 h, magnetic separation was performed, ethanol washing was performed, and deionized water washing was performed to obtain a reddish brown micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder; the micron-sized alumina-coated iron oxide powder was composed of iron oxide and aluminum oxide, the mass fraction of iron element was 67.37 wt%, the mass fraction of aluminum element was 2.85 wt%, and the mass fraction of oxygen element was 29.78 wt%; the particles of the alumina-coated oxide powder were spherical and the particle size was 5~7.5 µm.

(2.2) Place the micron-sized alumina-coated iron oxide powder in a flowing hydrogen atmosphere, heat it to 550 °C at a heating rate of 5 °C/min, and keep it at that temperature for 4 h; then cool it naturally to obtain micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder.

Figure 9 is a SEM photo of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 2. It can be seen that the powder is composed of spherical particles with a complete spherical morphology and a particle size of about 5-7 μm. At the same time, due to the escape of O element during the reduction process, some holes appear inside the particles with a pore size of about 10-40 nm.

FIG10 is an XRD spectrum of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 2. It can be seen that the diffraction peaks are sharp, indicating that the powder has high crystallinity. The diffraction peaks at 44.7°, 65.0° and 82.3° are characteristic diffraction peaks of Fe, indicating that there is a single Fe with high crystallinity in the powder.

FIG. 11 is an EDS image of the micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder prepared in Example 2. As can be seen from the image, the Al element is evenly distributed on the surface of the particles to form an Al ₂ O ₃ coating layer.

Example 3

The preparation steps of an iron-based micropowder with high magnetic permeability and low high-frequency loss are as follows:

(1) Preparation of micron-sized iron oxide (Fe ₂ O ₃ ) powder

(1.1) Mix equal volumes of glycerol and deionized water and divide the mixture into two solutions, namely solution A and solution B;

Dissolve 1.06 g of anhydrous sodium acetate in 25 ml of solution A to obtain anhydrous sodium acetate solution; dissolve 1.99 g of ferrous chloride tetrahydrate in 25 ml of solution B to obtain ferrous chloride tetrahydrate solution; add the anhydrous sodium acetate solution dropwise to the ferrous chloride tetrahydrate solution under magnetic stirring to form a gray-green mixture; keep the mixture in a reactor at 180°C for 12 h; cool, separate magnetically, wash with ethanol, and wash with deionized water to obtain a brown precipitate; vacuum dry the brown precipitate at 50°C to obtain micron-sized ferrous carbonate (FeCO ₃ ) powder; the ferrous carbonate powder is brown-brown, and the particles of the ferrous carbonate powder are spherical with a particle size of 6~8 µm.

(1.2) Micron-sized ferrous carbonate powder was heated to 700 °C in air at a heating rate of 5 °C/min and kept at that temperature for 3 h. The mixture was then cooled naturally to obtain reddish-brown micron-sized iron oxide (Fe ₂ O ₃ ) powder with a particle size of 5-7 µm.

(2) Preparation of micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder

(2.1) 0.2 g of aluminum nitrate nonahydrate was dissolved in 100 ml of ethanol to obtain an aluminum nitrate nonahydrate solution; 1 g of reddish brown micron-sized iron oxide (Fe ₂ O ₃ ) powder was added to the aluminum nitrate nonahydrate solution and mechanically stirred to obtain a mixed material C; 1 g of anhydrous sodium carbonate was dissolved in 25 ml of deionized water and added dropwise to the mixed material C, the pH value was adjusted to 4, the reaction was performed for 4 h, magnetic separation was performed, ethanol washing was performed, and deionized water washing was performed to obtain a reddish brown micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder; the micron-sized alumina-coated iron oxide powder was composed of iron oxide and aluminum oxide, the mass fraction of iron element was 67.37 wt%, the mass fraction of aluminum element was 2.85 wt%, and the mass fraction of oxygen element was 29.78 wt%; the particles of the alumina-coated oxide powder were spherical and the particle size was 5~7.5 µm.

(2.2) Place the micron-sized alumina-coated iron oxide powder in a flowing hydrogen atmosphere, heat it to 600 °C at a heating rate of 5 °C/min, and keep it at that temperature for 4 h; then cool it naturally to obtain micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder.

Figure 12 is a SEM photograph of the micron-sized aluminum oxide-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder prepared in Example 3. It can be seen that the powder is composed of spherical particles, the spherical morphology remains intact, and the particle size is about 5-6.5 μm. However, as the reduction temperature increases, the escape of the O element becomes more intense, and more holes appear in the particles, with a pore size of about 50-80 nm.

FIG13 is an XRD spectrum of the micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder prepared in Example 3. It can be seen that the diffraction peaks are sharp, indicating that the powder has high crystallinity. The diffraction peaks at 44.7°, 65.0° and 82.3° are characteristic diffraction peaks of Fe, indicating that there is a single Fe with high crystallinity in the powder.

FIG. 14 is an EDS image of the micron-sized aluminum oxide-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder prepared in Example 3. It can be seen from the image that after high-temperature reduction, there is still an Al ₂ O ₃ insulating layer on the surface of the particles.

FIG15 is a graph showing the element contents of the micron-sized aluminum oxide-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powders prepared in Examples 1, 2, and 3. It can be seen that the content of the Fe element gradually increases with the increase in the reduction temperature. Specifically, the mass fraction of the Fe element is 75-95 wt%, the mass fraction of the Al element is 2.5-4.0 wt%, and the mass fraction of the O element is 5.5-11.5 wt%.

Figure 16 is a hysteresis loop diagram of the micron-sized aluminum oxide-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powders prepared in Examples 1, 2 and 3. It can be seen that the powders prepared in Examples 1, 2 and 3 all exhibit obvious soft magnetic characteristics, and their saturation magnetizations are 156.46, 174.49 and 172.37 emu/g, respectively, and their coercive forces H _c are 181.85, 142.09 and 81.89 Oe, respectively.

Figure 17 is a density diagram of magnetic ring samples prepared from micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powders and commercially available high magnetic permeability carbonyl iron powder (D50 = 5 μm) prepared in Examples 1, 2, and 3. It can be seen that under the same pressing process, due to the presence of the lightweight Al ₂ O ₃ shell and pore structure, the density of the magnetic ring sample prepared from the micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder prepared in the embodiment of the present invention is lower, which helps to reduce the mass of electronic components.

FIG18 is a magnetic spectrum of the magnetic ring samples prepared from the micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) prepared in Examples 1, 2, and 3 of the present invention and the commercially available carbonyl iron powder (D50 = 5 μm). It can be seen that, in the case of similar particle sizes, the magnetic permeability of the magnetic ring prepared from the micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder prepared in Examples 1 and 2 is close to that of the magnetic ring prepared from the commercially available high magnetic permeability carbonyl iron powder, while the magnetic permeability of the magnetic ring prepared from the micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder prepared in Example 3 is about 15.59, which is significantly higher than the commercially available carbonyl iron powder magnetic ring. Obviously, the micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder prepared in the present invention has the characteristic of high magnetic permeability in the MHz frequency range.

FIG19 is a graph showing the magnetic loss factor of the magnetic ring samples prepared from the micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powders prepared in Examples 1, 2, and 3 of the present invention and the commercially available carbonyl iron powder. It can be seen that in the frequency range above 16 MHz, the magnetic loss factors of the magnetic ring samples prepared from the micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powders prepared in the three examples of the present invention are all lower than those of the samples prepared from the commercially available carbonyl iron powder, and the range is 0.008-0.013. Obviously, the micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powders prepared in the present invention have the characteristics of low loss in the high frequency range.

It will be easily understood by those skilled in the art that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (2)

1. A method for preparing an iron-based micropowder with high magnetic permeability and low high-frequency loss, characterized in that the operating steps are as follows: (1) Preparation of micron-sized iron oxide (Fe ₂ O ₃ ) powder (1.1) Mix equal volumes of glycerol and deionized water and divide the mixture into two solutions, namely solution A and solution B; Dissolve 1.06 g of anhydrous sodium acetate in 25 ml of solution A to obtain anhydrous sodium acetate solution; dissolve 1.99 g of ferrous chloride tetrahydrate in 25 ml of solution B to obtain ferrous chloride tetrahydrate solution; Under magnetic stirring conditions, anhydrous sodium acetate solution was added dropwise to ferrous chloride tetrahydrate solution to form a gray-green mixture; the mixture was kept in a reactor at 180°C for 12 h; the mixture was cooled, magnetically separated, washed with ethanol, and washed with deionized water to obtain a brown precipitate; the brown precipitate was vacuum dried at 50°C to obtain micron-sized ferrous carbonate (FeCO ₃ ) powder; the ferrous carbonate powder was brown-brown, the powder particles were spherical, and the particle size was 6-8 µm; (1.2) Micron-sized ferrous carbonate (FeCO ₃ ) powder was heated to 700 ℃ in air at a rate of 5 ℃/min, kept at this temperature for 3 h, and cooled naturally to obtain reddish-brown micron-sized iron oxide (Fe ₂ O ₃ ) powder with a particle size of 5~7 μm; (2) Preparation of micron-sized alumina-coated iron (Fe@Al ₂ O ₃ ) powder (2.1) 0.2 g of aluminum nitrate nonahydrate was dissolved in 100 ml of ethanol to obtain an aluminum nitrate nonahydrate solution; 1 g of reddish brown micron-sized iron oxide (Fe ₂ O ₃ ) powder was added to the aluminum nitrate nonahydrate solution and mechanically stirred to obtain a mixed material C; 1 g of anhydrous sodium carbonate was dissolved in 25 ml of deionized water and added dropwise to the mixed material C, the pH value was adjusted to 4, the reaction was carried out for 4 h, magnetic separation was performed, ethanol washing was performed, and deionized water washing was performed to obtain a reddish brown micron-sized alumina-coated iron oxide (Fe ₂ O ₃ @Al ₂ O ₃ ) powder; the micron-sized alumina-coated iron oxide powder was composed of iron oxide (Fe ₂ O ₃ ) and aluminum oxide (Al ₂ O ₃ ), the mass fraction of iron element was 67.37 wt%, the mass fraction of aluminum element was 2.85 wt%, and the mass fraction of oxygen element was 29.78 wt%; the particles of the micron-sized alumina-coated iron oxide powder were spherical, and the particle size was 5~7.5 µm; (2.2) placing the micron-sized aluminum oxide-coated iron oxide powder in a flowing hydrogen atmosphere, heating the temperature to 400-700 °C at a heating rate of 5 °C/min, and keeping the temperature for 4 h; cooling the mixture naturally to obtain a micron-sized aluminum oxide-coated iron (Fe@Al ₂ O ₃ ) core-shell powder; The micron-sized alumina-coated iron powder is composed of iron and an alumina (Al ₂ O ₃ ) coating layer, the mass fraction of the iron element is 75-95 wt %, the mass fraction of the aluminum element is 2.5-4.0 wt %, the mass fraction of the oxygen element is 5.5-11.5 wt %, the powder particles are spherical, the particle size is 5-7 μm, the particle surface of the micron-sized alumina-coated iron powder is rough, and there is a pore structure with a pore size of 10-80 nm; the soft magnetic composite material magnetic ring is prepared by pressing the micron-sized alumina-coated iron powder and the resin powder in a mass ratio of 1:1, and the magnetic permeability is 12.85-15.59 in the frequency range of 1-30 MHz under a voltage of 1 V; the magnetic loss factor is 0.008-0.013 in the frequency range of 16-30 MHz. 2. The method for preparing an iron-based micropowder with high magnetic permeability and low high-frequency loss according to claim 1, characterized in that: in step (2), the speed of mechanical stirring is 400 r/min and the material temperature is maintained at 50°C.